A light-emitting diode (LED) is typically implemented as a two-lead semiconductor light source. An LED resembles a basic pn-junction diode, which emits light when activated. When a fitting voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light, corresponding to the energy of the photon, is determined by the energy band gap of the semiconductor. An LED is often small in area (e.g., less than 1 mm2), and integrated optical components may be used to shape its radiation pattern.
White light can be formed by mixing differently colored lights. The most common method is to use red, green, and blue (RGB); hence, the method is called multi-color white LEDs (sometimes referred to as RGB LEDs). RGB LEDs are commonly made to include three color components, a red LED component, a green LED component, and a blue LED component. The three color components can be separately lit to produce a desired color combination, including white light. The three color components can be combined into a single package and controlled as a combined RGB LED unit. RGB LEDs need electronic circuits to control the blending and diffusion of different colors by activating (or inactivating) the three color LED components. The individual color LED components typically have slightly different emission patterns leading to a variation of the color depending on direction. RGB LEDs are particularly interesting in many applications, because of the flexibility of mixing different colors. This mechanism also has higher quantum efficiency in producing white light by combining the red, green, and blue colors.
However, LEDs and RGB LEDs are mainly used as light-producing elements in various forms of information and image displays, televisions, computer monitors, mobile device displays, and the like. As such, conventional LEDs and RGB LEDs serve mainly as output devices and not as input or control devices.